Continuously regenerated and integrated suppressor and detector for suppressed ion chromatography and method

ABSTRACT

An integrated suppressor and detector for suppressed ion chromatography includes a stationary phase, a fluid flow path, at least first and second regeneration electrodes, and at least first and second sensor electrodes. Methods of suppressed ion chromatography using the integrated suppressor and detector are also described.

FIELD OF THE INVENTION

[0001] The present invention relates to the field of ion chromatography(IC), and, in particular, to a continuously regenerated, integratedsuppressor and detector for use in suppressed ion chromatography (SIC).

BACKGROUND OF THE INVENTION

[0002] Suppressed ion chromatography (SIC) is a commonly practicedmethod of ion chromatography which generally uses two ion-exchangecolumns in series followed by a flow through conductivity detector fordetecting sample ions. The first column, called the analytical orseparation column, separates the analyte ions in a sample by elution ofthe analyte ions through the column. The analyte ions are flowed throughthe analytical column via a mobile phase comprising electrolyte.Generally, a dilute acid or base in deionized water is used as themobile phase. From the analytical column, the separated analyte ions andmobile phase are then flowed to the second column, which is called thesuppressor or stripper. The suppressor serves two primary purposes: (1)it lowers the background conductance of the mobile phase by retaining(e.g., suppressing) the electrolyte of the mobile phase, and (2) itenhances the conductance of the analyte ions by converting the analyteions to their relatively more conductive acid (in anion analysis) orbase (in cation analysis). The combination of these two functionsenhances the signal to noise ratio, and, thus, improves the detection ofthe analyte ions in the detector. Accordingly, upon exiting thesuppressor, the analyte ions and suppressed mobile phase are then flowedto the detector for detection of the analyte ions. A variety ofdifferent types of suppressor devices and methods are discussed in U.S.Pat. No. 3,897,213; 3,920,397; 3,925,019; 3,926,559; and U.S. Ser. No.08/911,847. Applicants hereby incorporate by reference the entiredisclosure of these patent applications and patents.

[0003] As those skilled in the art will appreciate, both the mobilephase and the sample contain counterions of the analyte ions. Asuppressor operates by ion exchange of suppressor ions, which arelocated in the suppressor, with both the (1) the mobile phaseelectrolyte counterions and (2) the sample counterions. In anionanalysis, for example, the suppressor ions normally comprise hydroniumions and the mobile phase comprises electrolyte such as sodium hydroxideor mixtures of sodium carbonate and sodium bicarbonate. In cationanalysis, the suppressor ions normally comprise hydroxide ions, and themobile phase may comprise electrolytes such as hydrochloric acid ormethanesulfonic acid. The suppressor ions are located on a stationaryphase, which may be an ion exchange membrane or resin. As the mobilephase and sample (which contains both analyte ions and counterions ofthe analyte ions) are flowed through the stationary phase of thesuppressor, the electrolyte counterions in the mobile phase and thesample counterions are retained on the stationary phase by ion exchangewith the suppressor ions. When the suppressor ions are either hydroniumor hydroxide, ion exchange of the electrolyte counterions withsuppressor ions converts the mobile phase to water or carbonic acid,which are relatively non-conductive. On the other hand, the ion exchangeof sample counterions with suppressor ions (i.e., hydronium or hydroxideions) converts the analyte ions to their relatively more conductive acid(in anion analysis) or base (in cation analysis). Thus, the analyteions, which are now in their relatively more conductive acid or baseform, are more sensitive to detection against the less conductivebackground of the mobile phase.

[0004] However, unless the suppressor ions are continuously replenishedduring the suppression process, the concentration of suppressor ions onthe stationary phase is reduced. Eventually the suppressor will becomeexhausted and its suppression capacity is either lost completely orsignificantly reduced. Thus, the suppressor must be either replaced orregenerated. The need to replace or regenerate the suppressor isinconvenient, may require an interruption in sample analysis, or requirecomplex valving or regeneration techniques known in the art. One exampleof a known technique for regenerating a suppressor by continuouslyreplenishing suppressor ions is disclosed in U.S. Pat. No. 5,352,360.

[0005] In addition to the need for regenerating or replacing suppressorions, another problem associated with SIC is that a separate suppressorunit is usually required, and, therefore, the number of components inthe system is increased over traditional IC systems. Traditional ICsystems usually contain a mobile phase source, a pump, a sampleinjector, an analytical column and a detector for detecting the sampleions. In SIC, a separate suppressor unit is added to the system. This,in turn, increases the complexity of the system and also increasesextra-column volume which may decrease chromatographic resolution andsensitivity. Therefore, it would also be advantageous to have a systemof ion suppression chromatography which reduced the number of systemcomponents in traditional SIC systems.

[0006] Another problem associated with prior art SIC systems is that themobile phase is converted to a weakly ionized form, which renders themobile phase unsuitable for reuse. Thus, it would be advantageous if asystem of SIC were developed in which the mobile phase is converted backto its strongly ionized form after suppression and, thus, may be reused.

SUMMARY OF THE INVENTION

[0007] In its various aspects, the present invention is capable ofsolving one or more of the foregoing problems associated with SIC.

[0008] In one aspect of the present invention, an integrated suppressorand detector is provided. By “suppressor” it is meant a device that iscapable of converting the mobile phase to water or a weakly conductiveform such as, for example, sodium carbonate or bicarbonate to carbonicacid and the ions to be detected (e.g. the analyte ions) to either theiracid or base prior to detection. In this aspect of the invention, thesuppressor is further equipped with sensor electrodes for detecting theanalyte ions. By “integrated” it is meant that the suppressor anddetector are contained within the same housing so that fluid transferlines between a separately housed suppressor and detector areunnecessary.

[0009] In a further aspect of the invention, a method of suppression ionchromatography is provided wherein the suppressor is continuouslyregenerated during suppression. The suppressor comprises a stationaryphase comprising suppressor ions which acts to suppress a mobile phasecontaining analyte ions to be detected. Electrolysis is performed on themobile phase to produce regenerating ions. The regenerating ions arethen flowed through the stationary phase to continuously replenish thesuppressor ions lost during suppression. Preferably, electrolysis isperformed on water present in the mobile phase.

[0010] In another aspect of the invention, an integrated suppressor anddetector is provided. The integrated suppressor and detector comprisesat least first and second regeneration electrodes and a fluid flow pathextending between the first and second regeneration electrodes. Astationary phase comprising suppressor ions is positioned in the fluidflow path. The integrated suppressor and detector further comprises atleast first and second sensor electrodes, in an electrical communicationwith a measuring device for recording analyte ions detected by thesensor electrodes.

[0011] In yet another aspect of the invention, a method of suppressionion chromatography is provided wherein the suppressed mobile phase isconverted back to its strongly ionized state after suppression. Thus,the mobile phase is recycled and may be reused.

DESCRIPTION OF THE DRAWINGS

[0012]FIG. 1 is a schematic view of a suppressor ion chromatographysystem incorporating the integrated suppressor and detector of theinvention.

[0013]FIG. 2 is a cross-section view of integrated suppressor anddetector according to one aspect of the invention taken along line 2-2of FIG. 3a.

[0014]FIG. 3a is a side perspective view of an integrated suppressor anddetector according to one aspect of the invention.

[0015]FIG. 3b is a cross-section view taken along line B-B of FIG. 3a.

[0016]FIG. 4 is an exploded perspective view of an integrated suppressorand detector according to another aspect of the invention.

[0017]FIG. 4a is a side view of an integrated suppressor and detectordepicted in FIG. 4.

[0018]FIG. 4b is a cross-sectional view of an integrated suppressor anddetector.

[0019] FIGS. 5-7 are chromatograms using an apparatus and methodaccording to the invention and are referred to in the examples.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

[0020]FIG. 1 illustrates an IC system using the integrated suppressorand detector of the present invention. The IC system comprises a mobilephase source 10, a pump 11, a sample injector 12 and an analyticalcolumn 14, all in fluid communication. The pump 11, sample injector 12and analytical column 14 may be selected from the variety of types knownby those skilled in the art. For example, preferred pumps include theALLTECH 526 pump available from ALLTECH ASSOCIATES, INC. (Deerfield,Ill.). Preferred analytical columns include the ALLTECH ALLSEP orUNIVERSAL CATION COLUMNS. Preferred sample injectors include theRHEODYNE 7725 injection valve.

[0021] An integrated suppressor and detector 16 in fluid communicationwith the analytical column 14 is further provided. As discussed below,the suppressor and detector 16 is connected to a power source 18 and ameasuring device 20. Preferred power sources include the KENWOODPR36-1.2A. A preferred measuring device is a conductivity detector suchas the OAKTON ¼ DIN Conductivity and Resistivity Controllers (OAKTON 100Series). Another suitable measuring device for use with the presentinvention is an electrochemical detector. The measuring device 20measures or records the analyte ions detected by sensor electrodes inthe integrated suppressor and detector 16.

[0022] In operation, the direction of fluid flow is as follows. Themobile phase is flowed from mobile phase source 10 by pump 11 throughinjection valve 12 to analytical column 14 to suppressor and detector16. Upon exiting the suppressor and detector 16, the mobile phase isflowed through recycling valve 19, which directs fluid flow either towaste or back to mobile phase source 10 as discussed below. Therecycling valve 19 is preferably a three-way valve.

[0023] With reference to FIG. 2, the suppressor and detector 16comprises a first regeneration electrode 30 and a second regenerationelectrode 32. The regeneration electrodes are held in housing 17 of thesuppressor and detector 16 by a threaded nut (not shown). Seals 241 and241 a are preferably included to provide a fluid-tight seal betweenelectrodes 30 and 32 and housing 17. The seals 241 and 241 a arepreferably O-rings made from materials that are compatible with acidsand bases such as, for example, ethylene propylene. Preferably, theregeneration electrodes are flow-through electrodes. By flow-throughelectrodes, it is meant that the electrodes allow sample analyte ionsand mobile phase to flow therethrough. The electrodes are preferablymade from carbon, platinum, titanium, stainless steel or any othersuitable conductive, non-rusting material. The most preferred electrodesare made of platinum coated titanium, ruthenium oxide coated titanium,titanium nitride coated titanium, gold, or rhodium with an average poresize of between 0.1 μm and 100 μm. The first regeneration electrode 30and the second regeneration electrode 32 are connected to the powersource 18. A fluid flow path (indicated by arrows) is positioned betweenthe first and second regeneration electrodes. The fluid flow path maypreferably extend from the first regeneration electrode 30 to the secondregeneration electrode 32. The fluid flow path may be defined byinternal walls of housing 17. Housing 17 is preferably made from aninert material such as those disclosed in co-pending application Ser.No. 08/911,847. Also, as those skilled in the art will appreciate, thehousing 17 should be constructed from a relatively non-conductivematerial.

[0024] A stationary phase 39 is positioned in the fluid flow path. Thestationary phase 39 may comprise a variety of stationary phases known inthe art for suppressors. Such stationary phases include membranes andion exchange resins, for example. Preferably, the stationary phasecomprises ion exchange resin. In anion analysis, cation exchange resinwill be used. A preferred cation exchange resin is BIORAD AMINEX 50W-X12(which is a sulfonated polystyrene divinylbenzene 200-400 mesh). Othersuitable stationary phases include DUPONT NAFION ion-exchange beads andmembranes and PUROLITE ion-exchange resins. During operation, thepreferred cation exchange resin comprises exchangeable hydronium ions.In cation analysis, anion exchange resin will be used. A preferred anionexchange resin is BIORAD AMINEX AG1-X8 100-200 mesh (which is aquaternary amine polystyrene divinyl benzene). During operation, thepreferred anion exchange resin comprises exchangeable hydroxide ions.

[0025] The suppressor and detector 16 also comprise at least two sensorelectrodes for detecting the analyte ions. In the present embodiment,two sensor electrodes, first sensor electrode 37 and second sensorelectrode 38 are shown. The first and second sensor electrodes arepreferably located in the fluid flow path between first regenerationelectrode 30 and second regeneration electrode 32. The first and secondsensor electrodes preferably comprise either platinum-wire or anotherelectrochemically inert material such as gold, rheuthinium oxide orplatinum, either neat or plated or suitable substrates such as titaniumor stainless steel. The sensor electrodes 37 and 38 are preferably inelectrical communication with a measuring device (not shown) forrecording the analyte ions detected by the sensor electrodes. Withreference to FIGS. 3a and 3 b, the first and second sensor electrodespreferably have a serpentine configuration across a cross-section of theflow path. In particular, two rows of four holes each (see referencenumerals 40-43 and 44-47, respectively) are provided. The first sensorelectrode 37 is weaved through holes 40-43 and the second electrode 38is weaved through holes 44-47 formed in housing 17. Most preferably, atleast a portion of the stationary phase 39 will be positioned in thefluid flow path between the first and second sensor electrodes. Finally,an end of each of the first sensor electrode 37 and the second sensorelectrode 38 is in electrical communication with the measuring device20. Preferably, the suppressor and detector 16 is 21 mm×7.5 mm internaldiameter. In a preferred aspect of the invention, the distance betweenthe regeneration electrode 30 and sensor electrode is about 7.95 mm. Thedistance between regeneration electrode 32 and sensor electrode 38 isabout 11.8 mm. The distance between sensor electrodes 37 and 38 is about1.4 mm.

[0026] The system of the present invention may be used for detectinganalyte ions comprising anions or cations. Moreover, a variety of mobilephases may be used. For cation analysis, preferred mobile phases includeaqueous solutions of either hydrochloric acid, methanesulfonic acid orsulfuric acid. For anion analysis, preferred mobile phases includeaqueous solutions of either sodium hydroxide or sodiumcarbonate/bicarbonate. Preferably, the mobile phase is aqueous and,therefore, no separate water-source is required. The operation of thesuppressor and detector 16 will be described with reference to FIG. 2for anion analysis and a mobile phase consisting of an aqueous solutionof sodium hydroxide. As those of ordinary skill in the art will quicklyappreciate, the invention may easily be adapted for cation analysisalso.

[0027] To prepare the system for operation, the mobile phase should beflowed through the system and the power source turned on. Once thebaseline created by the mobile phase has stabilized, the system is readyfor ion analysis. A sample, which contains analyte anions to be detectedand analyte counterions (e.g., cations), is injected at sample injector12 and flowed to analytical column 14 by pump 11. The analyte anions areseparated (or resolved) in analytical column 14 and then flowed with themobile phase to suppressor and detector 16.

[0028] In anion analysis, the stationary phase 39 in the suppressor anddetector 16 is preferably ion exchange resin comprising exchangeablehydronium ions. The sample which contains the previously separatedanalyte anions from analytical column 14 along with the analytecounter-cations are flowed with the mobile phase to the suppressor anddetector 16. The analyte counter-cations are retained on the stationaryphase 39 by ion exchange with the hydronium ions. Thus, the analyte ionsare converted to their relatively more conductive acid according to thefollowing formula:

I⁺X⁻+stationary phase-H⁺=HX+stationary phase-I⁺

[0029] (where X⁻ comprises analyte anions selected from, for example,Cl, NO₂, Br, etc.; and I⁺ are analyte counterions selected from, forexample, K⁺). Also, the sodium ions in the mobile phase may be retainedon the stationary phase 39 by ion exchange with the hydronium ions.Thus, the mobile phase is converted to the relatively non-conductivewater according to the following formula:

NaOH+stationary phase-H⁺=H₂O+stationary phase-Na⁺

[0030] In addition to the foregoing reactions, a current is createdacross stationary phase 39, first regeneration electrode 30 and secondregeneration electrode 32 by power source 18. The water from the aqueousmobile phase undergoes electrolysis to form regenerating ions at thefirst regeneration electrode 30 and second regeneration electrode 32,respectively. In anion analysis, the first regeneration electrode 30 isthe anode at which regeneration ions consisting of hydronium ions aregenerated. The second regeneration electrode 32 is the cathode at whichhydroxide ions are generated. As those skilled in the art willrecognize, in cation analysis the polarity is reversed and the upstreamregeneration electrode will be the cathode and the regenerating ionswill comprise hydroxide ions.

[0031] In this embodiment, the regenerating hydronium ions generated atthe first regeneration electrode 30 are then flowed through thestationary phase 39 thereby continuously regenerating the stationaryphase 39 by ion exchange of the regenerating hydronium ions with theretained sodium ions and analyte counter-cations according to thefollowing formulas:

H⁺+stationary phase-Na⁺=stationary phase-H⁺+Na⁺

H⁺+stationary phase-I⁺=stationary phase-H⁺+I⁺

[0032] The sodium ions released from the stationary phase 39 are flowedto the second regeneration electrode 32 where they combine with theregeneration hydroxide ions to yield aqueous sodium hydroxide. If thereare no analyte anions or analyte counter-cations flowing from thesuppressor and detector 16, this aqueous sodium hydroxide may be flowedthrough recycling valve 19 and back to mobile phase source 10. In thisfashion, a self-regenerating mobile phase is also provided. If, however,there are analyte anions or analyte counter-cations exiting thesuppressor and detector 16 along with the aqueous sodium hydroxide, thefluid flow is preferably directed to waste. Preferably, the system willinclude a solvent recycling device, such as the ALLTECH SOLVENT RECYCLER3000, which will sense the absence of analyte anions or analytecounter-cations and automatically direct the flow of the regeneratedsodium hydroxide mobile phase to source 10. In contrast, if the solventrecycling device detects the presence of sample ions or counter-ions, itwill direct the fluid flow to waste.

[0033] In a preferred embodiment of the invention, the analyte ions aredetected while in the suppressor and detector 16. Still with referenceto the anion analysis discussed above, there is a high concentration ofhydronium ions proximate to sensor electrodes 37 and 38. The source ofthese hydronium ions are the regeneration hydronium ions generated atfirst regeneration electrode 30 and the hydronium ions released from thestationary phase 39 by ion exchange with the sodium ions and analytecounter-cations. Preferably, the concentration of hydronium ions isgreater than the concentration of sodium ions or analyte counter-cationsproximate the sensor electrodes. By optimizing the concentration ofhydronium ions, the amount of sample ions in the acid form is likewiseoptimized, which leads to better detection sensitivity.

[0034] As discussed above, a current is applied across the stationaryphase 39 for generating the regeneration ions. When the analyte anionsin their acid form are flowed to the sensor electrodes, a change in thecurrent is detected by the sensor electrodes. This change in current,and the extent of the change, reflects the amount of analyte ion presentin the suppressor and detector 16. Preferably, the change in current isdetected by a measuring device 20 and recorded.

[0035] In an alternate embodiment of the invention (not shown), theseparate sensor electrodes may be omitted and the first and secondregeneration electrodes 30 and 32 may also function as the sensorelectrodes as previously described above. In yet another embodiment ofthe invention (not shown), one of the sensor electrodes may be omittedand one of the regeneration electrodes may perform the function of botha regeneration electrode and a sensor electrode as discussed above.

[0036] Another aspect of the invention using an ion-permeable ionexchange membrane is depicted in FIG. 4. FIG. 4 is an exploded view ofan alternative configuration for the suppressor and detector.Suppressors using ion exchange membranes having this generalconfiguration (except for the sensor electrodes) are known in the art.Examples of these suppressors are disclosed in U.S. Pat. Nos. 5,248,426and 5,352,360, the disclosure of which are hereby incorporated byreference. In the embodiment depicted in FIG. 4, a first regenerationelectrode 130 and a second regeneration electrode 132 are provided. Theelectrodes may be constructed from the same materials as previouslydiscussed. However, as those of ordinary skill in the art willappreciate, the electrodes 130 and 132 preferably are not flow-throughelectrodes in this embodiment. First and second ion exchange membranes134 and 135 are also provided. First and second ion exchange membranespreferably comprise exchangeable ions selected from the group consistingof hydronium and hydroxide ions. Positioned between ion exchangedmembranes 134 and 135 and electrodes 130 and 132 are a first set ofspacers 130 a and 132 a, which define fluid flow paths providing fluidcommunication between electrode 130 and membrane 134 and electrode 132and membrane 135, respectively. Also, adjacent first and second ionexchange membranes are second set of spacers 140 and 141, respectively,which define a fluid flow path 145. The spacers 130 a, 132 a, 140 and141 preferably may comprise a permeable, inert material such as a TEFLONmembrane. Alternatively, the spacers may comprise an inert sheetconstructed from MYLAR, PTFE, polypropylene or the like which has beencut to provide fluid communication between membranes 134 and 135 and thefluid flow path 145 as well as between electrodes 130 and 132 andmembranes 134 and 135, respectively. Positioned in spacers 140 and 141are sensor electrodes 137 and 138, respectively, which may be aspreviously described. Preferably, the sensor electrodes 137 and 138 arepositioned at the downstream end of fluid flow path 145. As thoseskilled in the art will appreciate, the sensor electrodes will bepositioned so that they are in fluid communication with the fluid flowpath 145. Also, in the configuration depicted in FIG. 4, in addition tofluid flow path 145, fluid flow paths 145 a and 145 b are defined by thecombination of spacer 130 a and membrane 134 and spacer 132 a andmembrane 135, respectively.

[0037] In operation, the suppressor and detector depicted in FIG. 4operates along the same general principles as previously discussed withrespect to the embodiment depicted in FIGS. 1-3 b. However, whereas thedirection of current flow is generally parallel to the direction offluid flow in the embodiment depicted in FIGS. 1-3 b, the direction ofcurrent flow is generally perpendicular to the direction of fluid flowin the embodiment depicted in FIG. 4. Thus, in anion analysis, forexample, the sample comprising analyte ions (anions) and samplecounterions along with an aqueous mobile phase comprising electrolytecounterions are flowed to suppressor and detector 116 and fluid flowpath 145. The water in the mobile phase undergoes electrolysis. In thisembodiment, electrode 130 may be the anode and electrode 132 may be thecathode. Thus, hydronium ions are generated at electrode 130 andhydroxide ions are generated at the electrode 132. As the analyte ionsand mobile phase are flowed through fluid flow path 145, the analytecounterions and mobile phase electrolyte counterions are retained on themembranes 134 and 135 by ion exchange with hydronium ions. The hydroniumions, both from the membranes 134 and 135 and the electrolysis productof water, migrate to fluid flow path 145 converting the analyte ions totheir acid and the mobile phase to water. The analyte anions in theiracid form may then be detected by sensor electrodes 137 and 138.

[0038] Additionally, the hydronium ions from the electrolysis willreplace the retained electrolyte and sample counterions on membranes 134and 135 thereby regenerating these membranes. The released electrolytecounterions may then recombine with the hydroxide ions generated by theelectrolysis at electrode 132 to regenerate the mobile phase, which maybe reused as described previously.

[0039] Although the sensor electrodes 137 and 138 may be positioned inone of the fluid flow paths 145, 145 a or 145 b, preferably, the sensorelectrodes will be placed in path 145. Also, the sensor electrodes 137and 138 are in electrical communication with a measuring device (notshown) for recording the detected analyte ions.

[0040] The devices and systems disclosed in U.S. Pat. Nos. 5,248,426 and5,352,360 may be adapted for use according to yet another aspect of theinvention. FIG. 4b shows a cross-section of a suppressor and detector316 having the configuration of the suppressor and detector depicted inFIG. 4, except that the path of fluid flow through the suppressor anddetector is modified. The electrodes 330 and 332, membranes 334 and 335and spacers 330 a, 332 a, 340 and 341 may be as described with respectto FIG. 4. The sensor electrodes 337 and 338 are positioned in the fluidflow path 345. Preferably, the sensor electrodes are positioned towardsthe downstream end of fluid flow path 345. However, in this embodiment,the path of fluid flow is through fluid flow path 345 and then backthrough fluid flow paths 345 a and 345 b in a direction of flow oppositethe direction of fluid flow through path 345.

[0041] With reference to FIG. 4b, in anion analysis, for example, anaqueous mobile phase comprising electrolyte is flowed through fluid flowpath 345 to fluid flow paths 345 a and 345 b A sample comprising analyteanions and analyte counterions is flowed through fluid flow path 345.The analyte counterions are retained on membranes 334 and 335 by ionexchange with hydronium ions. Similarly, the mobile phase electrolytesare retained on membranes 334 and 335 by ion exchange with hydroniumions. The released hydronium ions from membranes 334 and 335 and thehydronium ions generated at electrode 330 from the electrolysis of waterin the mobile phase combine with the analyte anions in the fluid flowpath 345 forming the acid of the analyte anions and converting themobile phase to water. The analyte anions, in their acid form, are thendetected in the fluid flow path 345 by sensor electrodes 337 and 338,which are preferably in electrical communication with a measuring device(not shown).

[0042] The analyte anions (in their acid form) and water is then flowedto fluid flow paths 345 a and 345 b. This provides a continuous supplyof water for the electrolysis. Also, the continuous supply of hydroniumions generated at electrode 330 replaces the retained sample andelectrolyte counterions on membranes 334 and 335, thereby continuouslyregenerating these membranes. The displaced sample and electrolytecounterions (cations) migrate towards electrode 332 (where hydroxideions are generated by the electrolysis) to flow path 345 b and out ofsuppressor and detector 316. The effluent from flow paths 345 a and 345b may be flowed to waste.

[0043] As those skilled in the art will appreciate, one of the spacers140 and 141 (FIG. 4) or spacers 340 and 341 (FIG. 4b) may be eliminated.Thus, instead of two spacers, one spacer defining a fluid flow path 145(FIG. 4) or 345 (FIG. 4b) may be used.

EXAMPLE 1

[0044] In this example, sample anions were analyzed according to amethod of the invention using a suppressor and detector according to theembodiment of FIG. 2. The following items were used. The analyticalcolumn was an ALLTECH ALLSEP anion column, 100×4.6 mm ID packed withmethacrylate-based quaternary amine anion exchange resin. The mobilephase was aqueous 0.7 mM sodium bicarbonate/1.2 mM sodium carbonate. Themobile phase flow rate was 0.5 mL/min. The integrated suppressor anddetector was packed with high capacity polystyrene divinylbenzene basedsulfonated cation exchange resin (BIORAD AMINEX 50W-X12 200-400 mesh).The integrated suppressor and detector was a column 21×7.5 mm ID. Thedistance between the inlet regenerating electrode and the first sensorelectrode was 7.95 mm. The distance between the second sensor electrodeand the outlet regenerating electrode was 11.8 mm. The distance betweenthe first and second sensor electrodes was 1.4 mm. The conductivitydetector was an OAKTON 1000 series ¼ DIN conductivity and resistivitycontroller. The power source was a KENWOOD PR 32-1.2A regulated DC powersupply. The amount of current applied was 100 mA (corresponding voltageof 15 V).

[0045]FIG. 5 is the chromatogram for a sample anion mixture (100 μL).The following peaks correspond to the following anions: 1—flouride (10ppm); 2—chloride (20 ppm); 3—nitrite (20 ppm); 4—bromide (20 ppm);5—nitrate (20 ppm); 6—phosphate (30 ppm); and 7—sulfate (30 ppm).

EXAMPLE 2

[0046] In this example, the same equipment and conditions as in Example1 were used. FIG. 6 is the chromatogram for a sample anion mixture withthree repetitive injections of 100 μL each. The following peakscorrespond to the following anions: 1—chloride (10 ppm); and 2—sulfate(10 ppm).

EXAMPLE 3

[0047] In this example, sample cations were analyzed according to amethod of the invention shown in the embodiment of FIG. 2. The followingequipment and conditions were used. The analytical column was an ALLTECHUniversal cation column, 100×4.6 mm ID, packed with silica coated withpolybutadiene-maleic acid cation exchange resin. The mobile phase wasaqueous 3.0 mM methane sulfonic acid. The mobile phase flow rate was 0.5mL/min. The integrated suppressor and detector was packed withpolystyrene divinyl benzene quaternary amine resin (BIORAD AMINEXAG-1-X8 100-200 mesh). The integrated suppressor and detector had thedimensions as set forth in Example 1. The conductivity detector was anOAKTON 1000 series ¼ DIN conductivity and resistivity controllers. Acurrent of 200 mA was applied (corresponding voltage is 22 V).

[0048]FIG. 7 is a chromatogram for a sample cation mixture, 4 repetitiveinjections of 100 μmL each. The following peaks correspond to thefollowing cations: 1—lithium (1 ppm); 2—potassium (6 ppm); and3—magnesium (6 ppm).

[0049] It should be understood that the foregoing description of thepreferred embodiments and the examples are not intended to limit thescope of the invention. The invention is defined by the claims and anyequivalents.

We claim:
 1. An integrated suppressor and detector for detecting analyteions in a sample comprising: (a) a suppressor; and (b) at least a firstsensor electrode and a second sensor electrode positioned in thesuppressor for detecting the analyte ions.
 2. The integrated suppressorand detector of claim 1 further comprising ion exchange resin.
 3. Theintegrated suppressor and detector of claim 2 wherein at least a portionof the ion exchange resin is positioned between the first and secondsensor electrodes.
 4. The integrated suppressor and detector of claim 3further comprising a fluid flow path wherein the first and second sensorelectrodes are positioned in the fluid flow path.
 5. A method ofconducting suppression ion chromatography wherein a suppressor iscontinuously regenerated comprising: (a) providing a stationary phasecomprising suppressor ions; (b) providing an aqueous mobile phasecomprising analyte ions to be detected; (c) performing electrolysis onthe mobile phase; and (d) flowing regenerating ions through thestationary phase.
 6. The method of claim 5 wherein the regenerating ionsare selected from the group consisting of hydronium ions and hydroxideions.
 7. The method of claim 6 wherein the suppressor ions comprisecation exchange resin with exchangeable hydronium ions, and the analyteions comprise anions.
 8. The method of claim 6 wherein the suppressorions comprise anion exchange resin with exchangeable hydroxide ions, andthe analyte ions comprise cations.
 9. An integrated suppressor anddetector for use in conducting suppression ion chromatographycomprising: (a) at least a first regeneration electrode and a secondregeneration electrode, and a fluid flow path extending between thefirst and second regeneration electrodes; (b) a stationary phasecomprising suppressor ions positioned in the fluid flow path; (c) atleast first and second sensor electrodes positioned in the fluid flowpath; and (d) a measuring device in electrical communication with thefirst and second sensor electrodes.
 10. The integrated suppressor anddetector of claim 9 wherein the suppressor ions are selected from thegroup consisting of hydronium ions and hydroxide ions; the first andsecond sensor electrodes are positioned in the fluid flow path; and atleast a portion of the stationary phase is positioned between the firstand second sensor electrodes.
 11. The integrated suppressor and detectorof claim 10 wherein the first and second sensor electrodes compriseplatinum.
 12. The integrated suppressor and detector of claim 9 whereinthe first regeneration electrode and the second regeneration electrodeare also simultaneously the first and second sensor electrodes,respectively.
 13. The integrated suppressor and detector of claim 9wherein one of the first or second regeneration electrodes is alsosimultaneously one of the first or second sensor electrodes.
 14. Theintegrated suppressor and detector of claim 9 wherein the stationaryphase comprises an ion exchange membrane.
 15. The integrated suppressorand detector of claim 9 wherein the stationary phase comprises ionexchange resin.
 16. A method of detecting analyte ions using suppressionion chromatography comprising: (a) providing first and secondregeneration electrodes; (b) providing a fluid flow path with astationary phase comprising suppressor ions selected from the groupconsisting of hydronium ions and hydroxide ions, wherein the fluid flowpath extends between the first and second regeneration electrodes; (c)providing a first sensor electrode and a second sensor electrodepositioned in the fluid flow path; (d) converting the analyte ions inthe fluid flow path to either their acid or base; and (e) detecting theconverted analyte ions in the fluid flow path with the sensorelectrodes.
 17. The method of claim 16 wherein the analyte ions comprisecations and the cations are converted to their base by ion exchange ofanalyte counterions with suppressor ions comprising hydroxide ions. 18.The method of claim 16 wherein the analyte ions comprise anions and theanions are converted to their acid by ion exchange of analytecounterions with suppressor ions comprising hydronium ions.
 19. A methodof conducting suppression ion chromatography comprising: (a) providing astationary phase comprising suppressor ions selected from the groupconsisting of hydronium ions and hydroxide ions, wherein at least aportion of the stationary phase is positioned in a fluid flow pathpositioned between a first regeneration electrode and a secondregeneration electrode; (b) providing an aqueous mobile phase comprisinganalyte ions to be detected, analyte counterions and electrolyte; (c)flowing the mobile phase through the stationary phase; (d) suppressingthe mobile phase by ion exchange of the electrolyte with the suppressorions of the stationary phase; (e) converting the analyte ions in thefluid flow path to their acid or base by ion exchange of the analytecounterions ions with the suppressor ions of the stationary phase; (f)detecting the acid or base of the analyte ions located in the fluid flowpath; and (g) regenerating the stationary phase during step (c) byperforming electrolysis on the mobile phase.
 20. The method of claim 19wherein the analyte ions comprise anions, and the anions are convertedto their acid.
 21. The method of claim 19 wherein the analyte ionscomprise cations, and the cations are converted to their base.
 22. Themethod of claim 19 where the step of regenerating the stationary phasecomprises: conducting electrolysis of water; and flowing regeneratingions selected from the group consisting of hydronium ions and hydroxideions through the stationary phase.
 23. A method of conductingsuppression ion chromatography wherein a mobile phase is regeneratedcomprising: (a) flowing a mobile phase comprising electrolyte to asuppressor; (b) suppressing the mobile phase by ion exchange of theelectrolyte with suppressor ions selected from the group consisting ofhydronium ions and hydroxide ions; and (c) combining the electrolytewith regeneration ions selected from the group consisting of hydroxideions and hydronium ions.
 24. The method of claim 23 wherein theregeneration ions are produced by electrolysis of water in the mobilephase.